1. Field of the Invention
The present invention relates to a chip resistor and method of making the same.
2. Description of the Related Art
An example of prior art chip resistor is shown in FIG. 14 of the present application (See JP-A-2002-57009). The illustrated chip resistor R1 includes a resistor element 90 in the form of a chip made of metal, and a pair of electrodes 91 provided on the lower surface 90b of the resistor element with a gap 93 defined therebetween. Each of the electrodes 91 has a lower surface formed with a solder layer 92.
The chip resistor R1 is made by a method as shown in FIG. 15. First, two metal plates 90′ and 91′ as materials for the resistor element 90 and the electrodes 91 are prepared (a). Subsequently, the metal plate 91′ is laminated and bonded to the lower surface of the metal plate 90′ (b). The metal plate 91′ is then partially removed by machining to form a gap 93 (c). Thereafter, a solder layer 92′ is formed on the lower surface of the metal plate 91′ (d). Finally, the metal plate 90′, 91′ are cut (e). As a result, a desired chip resistor R1 is obtained.
Generally, a chip resistor is soldered to a printed circuit board, for example. In this case, it is preferable that part of the solder becomes a solder fillet adhering to an end surface of the resistor element of the chip resistor. Such a solder fillet serves to strongly bond the chip resistor to the circuit board and also to provide good conduction between the chip resistor and the circuit board. Further, by checking the presence or absence of the solder fillet from outside, it is possible to determine whether or not the chip resistor is properly bonded to the circuit board. Specifically, when a solder fillet is formed, the mounting of the chip resistor can be determined to be proper. When a solder fillet is not formed, it can be determined that the mounting of the chip resistor is probably improper.
In this way, a solder fillet has many advantages for a chip resistor. However, in the chip resistor R1 shown in FIG. 14, it is difficult to form a solder fillet on an end surface of the resistor element 90. This is because the resistor element 90 is made of an alloy to which solder is unlikely to adhere (which has low solder-wettability) such as Ni—Cu alloy, Cu—Mn alloy or Ni—Cr alloy.